For the installation on my laptop, where i have only one HDD with Win 7, the installer automatically detected my 64 GB free space and installed Ubuntu to this space and GRUB was properly setup for dualboot. (The first page of the installer already offered me the option to do so.) Now i want to install Ubuntu on my desktop PC where i have a slightly different setup: on my first HDD i have 320 GB where i have Win 7 installed. My second HDD (not partition!) of about 1 TB is split up into 896 GB for use in Windows (not another instance of Win 7!) and 128 GB free space where i want to install Ubuntu.

Will Ubiquity recognize Win 7 on my other HDD and install GRUB without problems, as i do not want to reinstall Windows ;)

It should recognize it. I know that with an empty drive install it will recognize it on another drive. The only difference here is that you already have Windows installed on the installation drive.
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Kris HarperAug 23 '11 at 19:10

But Windows is not on the same installation drive as Ubuntu will be -> wouldn't that be in contrast to your prediction?
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Christian IvicevicAug 23 '11 at 19:17

Maybe I've misunderstood. You've said "1 TB is split up into 896 GB for Windows and 128 GB free space where i want to install Ubuntu." So as I understand it you have one drive with Windows 7, and another drive with another instance of Windows, plus some free space. So the drive on which you want to install Ubuntu has Windows on it, no?
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Kris HarperAug 23 '11 at 19:20

Nope! The 1 TB drive is "for Windows" with my files but there exists only one instance of Windows on my first 320 GB drive.
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Christian IvicevicAug 23 '11 at 19:21